I've noticed no problems with my garden plants thus far so do I use an insecticide just as a preventative? When should I take action?
No. Doesn't do any good if nothing is there.
And the pesticides, when used indiscriminately, can do a great deal of harm to the non-target creatures around your garden.
Spraying an Insecticide around your garden when there is no problem is a waste of your time, energy, and money and unnecessarily exposes you to potential harmful materials and can kill off beneficials that are helping you control the insect pests that may be there but that you don't notice because they are under control.
Aside from that spraying any insecticide anytime is very detrimental to our environment since any time any poisons are sprayed they produce changes that we are not yet aware of.
Thank you all for the advice. I'm new to gardening and wasn't sure when insecticide use was necessary and am currently researching organic, non chemical solutions. Kindest regards!